Popillia japonica: what it is, and why it must be contained

What it is

Popillia japonica Newman is a scarab beetle native to Japan. It is a strong flier with great ecological plasticity, which lets it colonise large areas in a short time, with over 300 host plants spanning crops, turf, ornamental and forest plants.

Because of its spread capacity and potential impact, it is on the EPPO A2 list as a quarantine pest and, in 2019, was classified among the EU's priority pests — the second most critical for Europe.

How to recognise it

The adult is about 1 cm long (8–11 mm), with a bright metallic-green head and thorax and copper-coloured wing cases (elytra). The unmistakable feature is the five tufts of white hair along each side of the abdomen, plus two at the tip — absent in similar native beetles. It flies by day in summer and often gathers in groups on leaves, flowers and fruit.

Its life cycle

In Italy it completes a single generation per year and spends most of its life as a larva in the soil — the stage the detection dog finds.

1. summer

   Egg

   Females lay eggs a few centimetres deep in grassy, moist soils; they hatch in 1–2 weeks.

2. autumn–spring

   Larva

   The larva — a white, C-shaped grub — eats roots; it moves deeper to overwinter and rises again to feed in spring.

3. late spring

   Pupa

   It pupates in the soil; after a few weeks it is ready to emerge.

4. June–August

   Adult

   It emerges in summer, feeds and mates above ground, then restarts the cycle by laying new eggs.

A rapid spread in Italy

It was first found in Italy, and in mainland Europe, in July 2014 in the Ticino valley, between Lombardy and Piedmont. There, plant-health authorities recorded extremely high larval densities, exceeding 300 individuals per square metre.

Despite major containment efforts, by 2022 the infested area had passed 16,000 km² across Northern Italy and Southern Switzerland, with interceptions in the Netherlands and Germany and new outbreaks in Sardinia and Friuli-Venezia Giulia.

Why it is dangerous

The damage happens on two fronts, above and below the soil surface:

• Adults: devour the leaves, flowers and fruit of over 300 species — including grapevine, soybean, maize and orchards of peach, plum, apple and persimmon.
• Larvae: live in the soil and eat the roots, destroying lawns, turf and crops.
• Secondary damage: high larval densities attract predators (birds, moles, wild boar) that dig up the soil, worsening the damage to turf.

How it spreads

It spreads on two scales:

• Short distance, by flight: an adult covers about 2.3 km in 24 hours on average, up to 12 km. Gregarious behaviour favours aggregation and mating, and mated females are the first to colonise new areas.
• Long distance, with human help: through infested soil and plants and by hitchhiking on vehicles and goods. High-risk sites are nurseries, car parks, loading areas, fuel stations, ports and airports.

The advancing front moves at roughly 5.5 to over 13 km per year depending on habitat suitability: it gains about 1.5 km/year for every extra 10% of suitable land.

Why finding it early makes the difference

In the first years after arrival the population is low and hard to detect. It then grows logistically: adults reach 200–300 catches per trap per day after 4–5 years, peaking after 7–8 years.

Larvae in the soil are invisible to the naked eye. Detecting them early makes it possible to act before the spread turns exponential, contain outbreaks and cut down on treatments — and that is exactly where the detection dog comes in.

Regulation and management

As a quarantine pest, the presence of P. japonica triggers demarcated zones and restrictions on moving plants and soil (EU Reg. 2016/2031). Nurseries face specific requirements: physical protection of the site, removal of soil or treated growing media, and potting soil reused only after heat treatment.

Effective management is integrated, combining chemical means (limited active ingredients; attract-and-kill devices with long-lasting insecticide nets), physical means (nets, mulching, controlled water stress) and biological means (entomopathogenic nematodes Heterorhabditis bacteriophora and Metarhizium fungi), within a sustainable approach.